Solid-state time-delay switching circuit

ABSTRACT

There is provided a time-delay switching circuit for switching an alternating-voltage supply source across a load comprising an electronic control means, such as a triac, having a first, second, and control electrode, and exhibiting the characteristic of presenting a low impedance to current flow from the voltage source to the load when a forward biasing signal is applied to the control electrode; and, circuit means for applying a forward biasing signal to the control electrode of the electronic control means. The circuit means includes a transformer having a primary and a secondary winding wherein the secondary winding is connected between the first and control electrode of the electronic control means; first and second actuatable switching means for, when both are actuated, completing a circuit between the primary winding and a power supply source for energizing the primary winding; means for periodically, and at a given frequency, actuating the first actuatable switching means; switch means having a first and a second condition; and, circuit means being responsive to the condition of the switch means for actuating the second actuatable switching means at a predetermined period of time after the switch means is switched from the first condition to the second condition.

United States Patent [72] Inventors James J. Vandemore Gencseo, IIL;Donald E. Henry, Davenport, Iowa [2!] Appl. No. 812,487 [22] Filed Sept.27,1968 [45] Patented Augili, I971 [73] Assignee Gull & WesternIndustries New York, N.Y.

[54] SOLID-STATE TIME-DELAY SWITCHING CIRCUIT 7 Claims, 1 Drawing Fig.

[52] U.S. Cl 307/252, 307/275, 307/293, 307/305 [51] Int. Cl 03k 17/26[50] Field of Search 307/252, 293, 275, 305

[56] References Cited UNITED STATES PATENTS 3,053,995 9/ I962 Hallberg..307/275 3,471,716 10/1969 Dinger 307/275 Primary Examiner-Donald D.Forrer Assistant Examiner-David M Carter Attorney-Meyer, Tilberry andBody This application filed under rule 47.

ABSTRACT: There is provided a time-delay switching circuit for switchingan alternating-voltage supply source across a load comprising anelectronic control means, such as a triac, having a first, second, andcontrol electrode, and exhibiting the characteristic of presenting a lowimpedance to current flow from the voltage source to the load when aforward biasing signal is applied to the control electrode; and, circuitmeans for applying a forward biasing signal to the control electrode ofthe electronic control means. The circuit means includes a transformerhaving a primary and a secondary winding wherein the secondary windingis connected between the first and control electrode of the electroniccontrol means; first and second actuatable switching means for, whenboth are actuated, completing a circuit between the primary winding anda power supply source for energizing the primary winding; means forperiodically, and at a given frequency, actuating the first actuatableswitching means; switch means having a first and a second condition;and, circuit means being responsive to the condition of the switch meansfor actuating the second actuatable switching means at a predeterminedperiod of time after the switch means is switched from the firstcondition to the second condition.

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SOLID-STATE TIME-DELAY SWITCHING CIRCUIT The present invention relatesto the art of time-delay switching circuits, and, more particularly, tosuch circuits for gating an electronic device, such as a triac, intoconduction at a predetermined period of time after an actuating signalis supplied.

The present invention is particularly applicable as a control circuitfor a triac, and will be described with particular reference thereto,although it will be appreciated that the invention has broaderapplications and may be used with other similar switching devices.

Solid-state switching devices, which are triggered into conduction by agating signal, for controlling the voltage applied to a load have becomean important component in a wide variety of control applications, Onesuch device is a silicon controlled rectifier. These devices are limitedto use in permitting current conduction in one direction only;therefore, for alternating current applications it is necessary toemploy two silicon controlled rectifiers, poled in reverse directionswith the gates of each device separately triggered. More recently, adevice known as a-triac and described in Application Note 200.35, Man,1966 by General Electric Company, has been employed for controllingalternating current. The term triac is a generic term that has beengiven a three-electrode AC semiconductive switch.

Time-delay relays known heretofore for switching an alternating-voltagesupply source across a load, particularly when high-current capabilityis required, have included an electronic circuit, such as aresistor-capacitor circuit, for energizing an electromechanical loadrelay after a predetermined period of time to thereby couple the loadacross the source. As is well known, electromechanical load relaysinherently have certain limitations, to wit, relatively low speedoperation, unreliable operation in adverse environment, relatively shortlife due to contact pitting, et cetera.

The present invention contemplates a new and improved time-delay circuitfor controlling a switching device which overcomes all of the abovereferred-to problems, and others, and provides a circuit which is simplein construction.

In accordance with the present invention, there is provided a time-delayswitching circuit for switching an alternating voltage source across aload comprising an electronic control means having a first, second, andcontrol electrode, wherein the control means exhibits the characteristicof presenting a low impedance to current flow from the voltage source tothe load when a forward-biasing signal is applied to the controlelectrode; and, circuit means for applying a forward-biasing signal tothe control electrode. The circuit means includes a transformer having aprimary and a secondary winding, wherein the secondary winding isconnected between the first and control electrode; first and secondactuatable switching means for, when both are actuated, completing acircuit between the primary winding and a power supply source forenergizing the primary winding; means for periodically, and at a givenfrequency, actuating the first acluable switching means; switch meanshaving a first and a second condition; and circuit means beingresponsive to the condition of the switch means for actuating the secondactuatable switching means at a predetermined period of time after theswitch means is switched from the first condition to the secondcondition.

In accordance with a more limited aspect of the present invention, thecircuit means for actuating the second actuatable switching meansincludes a switch means for altering the condition that the electroniccontrol means attains at a predetermined period of time after the switchmeans is switched from the first condition to the second condition.

The principle object of the present invention is to provide asolid-state circuit for switching an alternating-voltage supply sourceacross a load at a predetermined period of time after actuation of aswitch.

Another object of the present invention is to provide a solidstatecircuit for switching an alternating-voltage source across a load at apredetermined period of time after receipt of an input signal.

Another object of the present invention is to provide a timedelayswitching circuit in which the condition of the output terminals priorto timing, during timing, and upon completion of timing may be alteredby varying the position of a switch.

A still further object of the present invention is to provide asemiconductor, time-delay switching circuit having a relatively highcurrent capability.

A further object of the present invention is to provide a time-delayrelay beingcapable of high-speed operation, reliable operation inadverse environments, and in which the life of the relay is independentof the number of switching operations.

Another object of the present invention is to provide a semiconductortime-delay switching circuit which is capable of operation at relativelyhigh temperatures, i.e., in excess of C.

A still further object of the present invention is to provide atime-delay circuit for actuating a switching device in which the gatingsignal takes the form of a short time-duration pulse to thereby increasethe ambient temperature at which the device is capable of operation.

A further object of the present invention is to provide an improvedtime-delay circuit for gating a triac into conduction.

These and other objects and advantages of the invention will becomeapparent from the following description of the preferred embodiment ofthe invention as read in conjunction with the accompanying drawing inwhich:

The FIG. is a schematic circuit diagram illustrating an electroniccontrol circuit for gating a triac into conduction after a predeterminedperiod of time in accordance with the preferred embodiment of thepresent invention.

Reference is now made to the drawing, wherein the showings are forpurposes of illustrating a preferred embodiment of the present inventionand not for purposes of limiting same, the FIG. illustrates a time-delaycontrol circuit for gating a triac, and generally comprises a timingcircuit T connected through a logic circuit L and blocking oscillatorcircuit 0 to the control electrode of a triac 10.

BLOCKING OSCILLATOR Blocking oscillator circuit 0, as is moreparticularly described in US. Pat. application, Ser. No. 730,212, filedApr. 16, 1968, and entitled High Temperature Semiconductor Switchingcircuit," includes aresistor 14 having one terminal connected to timingcircuit T and the other terminal connected through a capacitor 16 toground. Connected to the junction between resistor 14 and capacitor 16is one terminal of a resistor 18 having the other terminal thereofconnected through a capacitor 20 to ground. Also connected to thejunction between resistor 14 and capacitor 16 is one terminal of aprimary winding 22 of a transformer 24. Connected to the other terminal,or the positive-polarity indicated end, of primary winding 22 is thecollector of an NPN transistor 26 having its base connected through aresistor 28 to ground. Also connected to the base of transistor 26 isthe cathode of a diode 30 having its anode connected to one terminal ofa feedback winding 32 of transformer 24. The other terminal, or thepositive-polarity indicated end, of feedback winding 32 is connecteddirectly to the junction between resistor 18 and capacitor 20. Theemitter of transistor 26 is connected to one terminal of logic circuitL. One terminal of a secondary winding '34 of transformer 24 isconnected to the control electrode 36, or gate terminal, of triaclO, andthe other terminal, or posirive-polarity indicated end, of secondarywinding 34 is connected directly to a first terminal38 of triac 10. Acapacitor 40 is connected between the first terminal 38 and a secondterminal 42 of triac 10. Also, the first terminal 38 and secondterminal42 of triac 10. provide the output terminals 44 and 46,respectively.

TIMING CIRCUIT Timing circuit T includes an alternating-voltage supplysource S having one terminal connected directly to ground, and the otherterminal connected to the anode of a diode 50. The cathode of diode 50is connected through a capacitor 52 to ground, and through a resistor 54to one terminal of a potentiometer S6. The other terminal ofpotentiometer 56 is connected directly to the base of a unijunctiontransistor 58, and is also connected through a capacitor 60 to ground.The first base of unijunction transistor 58 is connected through aresistor 61 to ground, and the second base of this transistor isconnected through a resistor 62 to the junction between resistor 54 andpotentiometer 56. Also connected to the first base of unijunctiontransistor 58 is a control electrode 64 of a silicon controlledrectifier 66. The cathode of silicon controlled rectifier 66. isconnected directly to ground, and the anode of this device is connectedthrough a pair of series connected resistors 68 and 70 to the junctionbetween resistor 54 and potentiometer 56.

Connected to the base of unijunction transistor 58 is the anode ofadiode 72 having its cathode connected to the anode of a diode 74. Theanode of diode 74 is also connected to the junction between resistors 68and 70, and to the anode of a diode 76.

LOGIC CIRCUIT Logic circuit L includes a normally open switch S1 havingone terminal connected to the junction between resistor 54 andpotentiometer 56, and the other terminal connected through a resistor 80to the base of an NPN transistor 82. As may be readily apparent,normally open switch S1 may be deleted from the circuit and an externaldirect-current supply source could be coupled through resistor 80 totransistor 82, if it is desirable to actuate the circuit externally.

The base and emitter oftransistor 82 are connected through resistors 84and 86, respectively, to ground. The collectors of transistor 82 isconnected through a resistor 88 to the junction between resistor 54 andpotentiometer 56. Also connected to the collector of transistor 82 is aresistor 90, having the other terminal thereof connected directly to thebase of an NPN transistor 92. The base of transistor 92 is alsoconnected through a resistor 94 to ground, and the emitter of transistor92 is connected directly to ground. The collector of transistor 92 isconnected to the anode ofdiode 74.

Also connected to the collector oftransistor 82 is the anode ofa diode96 having its cathode connected through a resistor 98 to the base of anNPN transistor 100. The base oftransistor 100 is also connected througha resistor 102 to ground, and the emitter ofthis transistor is connecteddirectly to ground.

The collector of transistor 100 is connected through a resistor 104 tothe junction between resistor 54 and potentiometer 56. Also connected tothe collector of transistor 100 is the anode ofa diode 106 having itscathode connected to terminal 1 ofa rotary-type switch 108. Terminal 2of rotary switch 108 is connected to the junction between diode 96 andresistor 98, and to the cathode of diode 74. Terminal 3 of switch 108 isconnected directly to the cathode of diode 76.

The movable arm 4 of switch 108 is connected through a resistor 110 tothe base of an NPN transistor 112, and the base of this transistor isalso connected through a resistor 114 to ground. The emitter oftransistor 112 is connected directly to ground, and the collector ofthis transistor is connected to the emitter of transistor 26.

OPERATION OF BLOCKING OSCILLATOR CIRCUIT The signal supplied byalternating-voltage supply source S is rectified through the networkcomprised of diode 50, capacitor 52, resistors 54 and 14, and capacitor16, to thereby provide a direct-current signal which will chargecapacitor through resistor 18, and will also cause transformer 24 tobegin to store energy in primary winding 22. As energy is graduallystored in primary winding 22, a positive voltage of increasing amplitudeis induced in feedback winding 32 of the polarity indicated withreference to the polarity dot. The voltage induced in feedback winding32 is applied through diode 30 to gradually forward bias transistor 26into conduction. Once transistor 26 commences to conduct, capacitor 20rapidly discharges through primary winding 22 and transistors 26 and 112to ground, assuming transistor 112 is forward biased into conduction.

When capacitor 20 discharges through primary winding 22, a voltageimpulse of short duration is developed across primary winding 22 whichin turn induces a similar pulse in secondary winding 34, to therebyapply a short duration gating signal to control electrode 36 of triac10. This gating signal causes triac 10 to switch from an of to an "oncondition. In the on condition, a closed path is completed betweenterminals 44 and 46, which path will be maintained until analternatingvoltage signal supplying a load passes through approximatelya zero-voltage level. Because the gating pulse is of a very shortduration, excessive current is not applied to the control electrode 36of triac 10, and operation at high temperatures is made possible.

Also, upon saturation of the core of transformer 24, the induced currentthrough feedback winding 32 terminates, and the forward biasing signalapplied to transistor 26 terminates, to thereby cause this transistor toagain become reverse biased. Once transistor 26- becomes reverse biased,capacitor 20 will again begin to charge to thereby commence anothercycle of operation.

When transistor 112 is reverse biased, the oscillator circuit includingtransistor 26 will crease to oscillate since there will be no path forthe discharge of capacitor 20. Transistor 112 is actuated by the signalsupplied from timing circuit T and logic circuit L.

OPERATION OF TIMING AND LOGIC CIRCUITS Prior to the closure of normallyopen switch S1, transistor 82 is reverse biased to thereby causetransistors 92 and to become forward biased. When transistor 92 isforward biased, capacitor 60 will discharge and remain in a dischargecondition through diode 72 and transistor 92. Since transistor 82 isreverse biased, and transistor 100 is forward biased, a binary l signalwill appear at terminal 2, and a binary 0" signal will appear atterminal 1, respectively, of switch 108. By a binary O" signal is meanta signal equal to approximately ground potential, and by a binary lsignal is meant a signal of some positive potential. Since the anode ofdiode 76 is effectively grounded through transistor 92, the signalappearing at the cathode of diode 76, i.e., terminal 3 of switch 108will be a binary 0 signal.

Upon closure of normally open switch S1, the direct-current signaldeveloped by diode 50 and capacitor 52 is applied to the base oftransistor 82 to forward bias this transistor into conduction, therebycommencing a timing cycle. When transistor 82 becomes forward biased,transistor 92 will become reverse biased to thereby allow capacitor 60to commence charging through potentiometer 56. As is readily apparentthe impedance of potentiometer 56 may be varied to alter the timingcycle of operation. During the timing operation, transistor 100 willremain in a conductive state since a binary l signal is applied to thebase thereof through resistor 70, diode 74, and resistor 98. Sincetransistor 100 remains in a conductive condition, the signal appearingat terminal 1 of switch 108 will remain at a binary 0 signal level. Whentransistor 92 becomes reverse biased, a binary l signal will appear atthe anode of diode 74 to thereby apply a binary l signal to terminal 2of switch 108. Similarly, a binary 1" signal will appear at the anode ofdiode 76 to thereby cause the signal at terminal 3 of switch 108 tochange from a binary 0" signal to a binary l signal.

When the voltage developed across capacitor 60 attains a levelsufficient to cause unijunction transistor 58 to fire or avalanche,", avoltage will be developed across resistor 61 to thereby gate siliconcontrolled rectifier 66 into conduction. When silicon controlledrectifier 66 becomes conductive, a binary 0" signal will be applied tothe anode of diodes 74 and 76. Sincetransistor 82 remains in aconductive state after the of a timing cycle, a binary 0" signal will beapplied to the anode of diode 96. With a binary 0" signal applied to theanodes of diodes 74, 76 and 96, a binary 0" signal will appear atterminals 2 and 3 of switch 108.

In accordance with the preferred embodiment of the invention, the binarysignals appearing at terminals 1, 2, and 3 of switch 108 and theconditions of output terminals 44 and 46 during each of the timingphases are illustrated in Table l:

When a binary 0" signal appears at terminal 1 of switch 108, assumingmovable arm 4 is in the position as illustrated in the FIGURE, a binary0" signal will be applied to the base of transistor I12 thereby reversebiasing this transistor. If a binary l signal appears at terminal 1 ofswitch 108, transistor 112 will be forward biased into conduction,thereby cominencing operation of blocking oscillator circuit 0,

As is readily apparent, with movable arm 4 of switch 108 in the positionas illustrated in the FIGURE, a circuit is completed between terminals44 and 46 through triac at a predetermined time after closure of switch51. If, however, movable arm 4 of switch 108 is moved to terminal 2,upon closure of switch S1 a circuit will be completed between terminals44 and 46 until the completion of a timing cycle. lf movable arm ofswitch 108 is positioned at terminal 3, triac 10 will be conductive onlyduring the period of timing.

Although the invention has been shown in connection with a preferredembodiment, it will be readily apparent to those skilled in the art thatvarious changes in form, such as replacement of switch S1 with anexternal signal source, in order to provide external control of thecircuit, may be made without departing from the spirit and scope of theinvention as defined by the appended claims. I

We claim:

1. A time-delay switching circuit for switching an alternating voltagesource across a load comprising:

static switch means having a first, second, and control electrode, saidswitch means exhibiting the characteristic of presenting a low impedanceto current flow from said alternating voltage source to said load when aforward biasing signal is applied to said control electrode;

circuit means for applying a forward biasing signal to said controlelectrode including:

First circuit means for developing a signal from a saidalternating-voltage source;

generating and actuatable switching means coupled to said first circuitmeans, for, when both are actuated, applying a said forward biasingsignal to said control electrode of said static switch means;

means for actuating said generating means;

second circuit means having a first and second condition respectivelyproviding a first level signal and a second level signal;

a normally open switch for energizing said second circuit means fromsaid first circuit means for transferring it from first signal level tosecond signal level; and

third circuit means for actuating said actuatable switch coupled to saidactuatable switching means, and said control electrode of saidelectronic control means being coupled to said second circuit means.

3. A switching circuit as defined in claim 2 wherein said means foractuating said generating means is a means for periodically, and at agiven frequency, actuating said generating means, and includes atransformer having a primary and a secondary winding, said secondarywinding connected between said first and said control electrodes of saidstatic switch means; and, said generating and said actuatable switchingmeans coupled between said first circuit means and said primary windingof said transformer, for, when both are actuated, completing a circuitbetween said primary winding and said first circuit means.

4. A switching circuit as defined in claim 3 wherein said transformerincludes a feedback winding coupled between said first circuit means andsaid generating means;

said actuatable switching means has a first and a second condition; and,said third circuit means includes a switch means for altering thecondition of said actuatable switching means prior to and afteractuation.

5. In a triac switching circuit for switching an alternating voltagesource across a load after a predetermined period of time comprising:

circuit means for applying a forward biasing signal to a said triacincluding:

first circuit means for developing a signal from a saidaltemating-voltage source;

generating and actuatable switching means coupled to said first circuitmeans, for, when both are actuated, applying a said forward biasingsignal to a said triac;

means for actuating said generating means;

second circuit means for developing a signal having a first level and asecond level; and,

third circuit means coupling said signal developing means to saidactuatable switching means for actuating said actuatable switch means ata predetermined period of time after said signal attains a said secondlevel.

6. A circuit as defined in claim 5 wherein said means for periodicallyactuating said generating means includes a transformer having a primaryand a secondary winding, said secondary winding adapted to be connectedbetween a first and said control electrode of a saidtriac; saidgenerating and said actuatable switching means coupled between saidfirst circuit means and said primary. winding of said transformer, for,when both are actuated, completing a circuit between said primarywinding and said first circuit means;

and, said third circuit means includes electronic control means having afirst, second, and control electrode, said second electrode of saidelectronic control means being coupled to said actuatable switchingmeans, and said control electrode of said electronic control means beingcoupled to said second circuit means.

7. A circuit as defined in claim 6 wherein said transformer includes afeedback winding coupled between said first circuit means and saidgenerating means;

and said actuatable switching means has a first and a second condition;and, said third circuit means includes a switching means for alteringthe condition of said actuatable switching means prior to and afteractuation.

1. A time-delay switching circuit for switching an alternating voltage source across a load comprising: static switch means having a first, second, and control electrode, said switch means exhibiting the characteristic of presenting a low impedance to current flow from said alternating voltage source to said load when a forward biasing signal is applied to said control electrode; circuit means for applying a forward biasing signal to said control electrode including: First circuit means for developing a signal from a said alternating-voltage source; generating and actuatable switching means coupled to said first circuit means, for, when both are actuated, applying a said forward biasing signal to said control electrode of said static switch means; means for actuating said generating means; second circuit means having a first and second condition respectively providing a first level signal and a second level signal; a normally open switch for energizing said second circuit means from said first circuit means for transferring it from first signal level to second signal level; and third circuit means for actuating said actuatable switch means at a predetermined period of time after said signal attains a said second level.
 2. A switching circuit as defined in claim 1 wherein said static switch means is a triac having first and second electrodes adapted to be connected in series with an alternating voltage source and a load; and, said third circuit means includes electronic control means having a first, second, and control electrode, said second electrode of said electronic control means being coupled to said actuatable switching means, and said control electrode of said electronic control means being coupled to said second circuit means.
 3. A switching circuit as defined in claim 2 wherein said means for actuating said generating means is a means for periodically, and at a given frequency, actuating said generating means, and includes a transformer having a primary and a secondary winding, said secondary winding connected between said first and said control electrodes of said static switch means; and, said generating and said actuatable switching means coupled between said first circuit means and said primary winding of said transformer, for, when both are actuated, completing a circuit between said primary winding and said first circuit means.
 4. A switching circuit as defined in claim 3 wherein said transformer includes a feedback winding coupled between said first circuit means and said generating means; said actuatable switching means has a first and a second condition; and, said third circuit means includes a switch means for altering the condition of said actuatable switching means prior to and after actuation.
 5. In a triac switching circuit for switching an alternating voltage source across a load after a predetermined period of time comprising: circuit means for applying a forward biasing signal to a said triac including: first circuit means for developing a signal from a said alternating-voltage source; generating and actuatable switching means coupled to said first circuit means, for, when both are actuated, applying a said forward biasing signal to a said triac; means for actuating said generating means; second circuit means for developing a signal having a first level and a second level; and, third circuit means coupling said signal developing means to Said actuatable switching means for actuating said actuatable switch means at a predetermined period of time after said signal attains a said second level.
 6. A circuit as defined in claim 5 wherein said means for periodically actuating said generating means includes a transformer having a primary and a secondary winding, said secondary winding adapted to be connected between a first and said control electrode of a said triac; said generating and said actuatable switching means coupled between said first circuit means and said primary winding of said transformer, for, when both are actuated, completing a circuit between said primary winding and said first circuit means; and, said third circuit means includes electronic control means having a first, second, and control electrode, said second electrode of said electronic control means being coupled to said actuatable switching means, and said control electrode of said electronic control means being coupled to said second circuit means.
 7. A circuit as defined in claim 6 wherein said transformer includes a feedback winding coupled between said first circuit means and said generating means; and said actuatable switching means has a first and a second condition; and, said third circuit means includes a switching means for altering the condition of said actuatable switching means prior to and after actuation. 